Optical fiber connector

ABSTRACT

In the connection of the optical fiber wires, it is required to align each axis of two optical passages to be connected, to minimize the connection space, and to include a retaining mechanism capable of preventing any invasion of foreign materials, such as dust, vapor and water. A pair of ferrule holders  2  for retaining a pair of optical fiber wires  21  positioned opposed to each other through an adapter B are rotated simultaneously by rotating an outer ring  4  to correct the displacement of the axes of the optical fiber wires. Further, a rotating stopper portion  33  on the shaft of the ferrule holder  2  is moved in conjunction with an elastic rotating stopper plate  13  disposed at the adapter B to retain the corrected position. A silicone low crosslinking-density gel  41  having the refractive index substantially equal to that of the optical fiber wires  21  is filled in a connection space  32,  to minimize the connection space  32.  The function of the silicone low crosslinking-density gel  41  can cope with any variance of external environment to retain the junction of the optical fiber wires  21  and prevent any deterioration of optical transmittance.

TECHNICAL FIELD

The present invention relates to an optical fiber connector forconnecting an optical fiber wire (core, clad sections) to anotheroptical fiber wire according to a fixed type connecting technique or adetachable type connecting technique.

BACKGROUND ART

A first conventional technique for connecting an optical fiber wire toanother optical fiber wire is a fusion-bonding technique, in which theaxes of the optical fiber wires are aligned with each other at theirbutted portions, and the butted portions of the optical fiber wires arefused in the form of a fusion bonding. A fusion-bonding device is usedfor this technique. A second conventional technique is a fixed typeconnecting technique, in which optical fiber wires to be connected areembedded in advance within a fitting provided in a connection passage ofthe optical fiber wires, and the optical fiber wires are mechanicallyfixed by filling up an oil material, a grease material, an epoxy resinmaterial, or a state-of-the-art gel material in the connection space. Asplicer or an optical distributor is used for this technique. A thirdconventional technique is a detachable type connecting technique, inwhich a ferrule is fitted to each end of optical fiber wires, and theoptical fiber wires are mechanically butted through an adapter to bejoined each other. An optical fiber connector is used for thistechnique. In order to reduce connection loss, some optical fiberconnector uses a lens, an oil material, a grease material, or astate-of-the-art gel material in the connection space. (For example,Japanese Patent Laid-Open Publication No. Sho 56-110912 discloses anoptical fiber connector using a lens, Japanese Patent Laid-OpenPublication No. Sho 56-081807 disclosing an optical fiber connectorusing an oil material, and Japanese Utility Model Publication No. Hei04-043841 disclosing an optical fiber connection using a gel material.)

Fundamental requirements for connecting optical fiber wires are asfollows.

i) Two optical passages (cores) to be connected are positioned on thealigned axes of the optical fiber wires;

ii) The connection space is strictly small; and

iii) The retaining mechanism is capable of preventing any invasion offoreign materials such as dust, vapor or water.

From this point of view, the conventional connecting techniques have thefollowing disadvantages.

The first conventional technique or fusion-bonding technique satisfiesthe above three fundamental requirements. However, it is not detachabletype, and thereby cannot be used as a connector.

In the second conventional technique or fixed type connecting technique,it is required to employ a complicated mechanism and take a number ofassembling hours for fabricating and aligning the embedding portion ofthe optical fiber wires to satisfy the above fundamental requirements.In addition, the oil or grease enclosed in the connection space isinevitably run out or oxidized. The epoxy resin is not run out butinevitably oxidized. This technique is not detachable type, and therebycannot be used as a connector, resulting in limited application.

The third conventional technique or detachable type connecting techniqueuses the structure in which the ferrule is fitted to each end of theoptical fiber wires, and the optical fiber wires are mechanically buttedthrough an adapter to be joined each other. Thus, as compared with thefirst and second conventional techniques, this technique cannot satisfythe first and second fundamental requirements, and thereby the opticaltransmittance is inevitably reduced. While various polishing, such asplanar surface polishing, spherical surface polishing, or inclinedsurface polishing, has been applied to the end of the optical fiber wireto suppress this optical attenuation and improve the opticaltransmittance, the above first and second fundamental requirements arenot sufficiently satisfied.

DISCLOSURE OF THE INVENTION

The present invention provides an optical fiber connector capable ofsatisfying the aforementioned three fundamental requirements. A typicaloptical fiber connector includes FC-type and SC-type specified in JIS.While they have a difference in coupling arrangement, they commonly relyupon the machining accuracy of the ferrule and adapter to align the axesof optical fiber wires.

For example, in the FC-type optical fiber connector, or an optical fiberconnector for single mode optical fiber wires, on the assumption thateach of optical fiber wires has a standard dimension or size, a ferruleto be fitted to the optical fiber wire has an outside dimension of2.4995 mm with its tolerance of ±0.0005 mm, and a hole for passing theoptical fiber wire therethrough and having a diameter of 0.125 mm, inwhich the tolerance of the concentric circle with respect to the hole islimited to ±0.0014 mm. Further, an adapter for inserting the ferrulethereinto has an inner diameter of 2.501 mm with its tolerance of +0.003mm. The ferrule and the adapter are coupled by a connection nut withguiding them along two key grooves formed at a ferrule holder and theadapter, respectively.

The connector is made with these accurate numerical values. However,each connection loss actually measured at both ends of the connectorexhibits a significantly different value. Specifically, provided thatone end “a” of both ends of a single optical fiber connector is anentrance (transmit section) and the other end “b” is an outlet (receivesection), each of the ends is connected to a master cord. When comparingthe connection loss in case of using the end “a” as a junction with theconnection loss in case of using the end “b” as a junction, thedifference is up to about 0.15 dB. This is caused by the displacementwith respect to the axes of the optical fiber wires and the opticalattenuation in the connection space. By way of experiment, when using arotatable adapter and measuring with rotating the ferrule, thedifference between the above connection losses was reduced in all of 20samples. This proves that the difference is caused by the displacementwith respect to the axis. The conventional optical fiber connectors donot have any mechanism for correcting such displacement with respect tothe axes of the optical fiber wires.

In order to solve the aforementioned first problem, a mechanism forcorrecting such displacement with respect to the axes of the opticalfiber wires is achieved by making a ferrule holder rotatable, andproviding in the adaptor a mechanism for stopping the rotation of theferrule holder at a optimum value with measuring the connection loss andretaining the ferrule holder.

A connection space inevitably exists at the junction of two opticalfiber wires, i.e., between opposed ends of the optical fiber wires.While the oil or grease has been used to minimize this space, thisapplication is limited due to its functional drawback, such as runningout or oxidization. In order to solve the second problem, a transparentsilicone low crosslinking-density gel having a refractive indexsubstantially equal to that of the optical fiber wires is filled in theconnection space to use as a junction conductor.

The composition and physical property of the silicone lowcrosslinking-density gel are as follows.

1. Composition: silicone mixture

2. Refractive index: 1.465 ±0.005

3. Viscosity: between 100,000 cP or more and 150,000 cP inclusive orless

4. Appearance: transparent

5. Temperature: usable in the range of −20° C. to 120° C. substantiallyno variation at room temperature

6. Water absorbing property: water absorption to the composition is 0.1%or less

7. Hygroscopic property: substantially no hygroscopic property to thecomposition

8. Anti-dust: dust may attach to the surface, but does not penetrateinto the composition

9. Pressure resistance: freely deformable to pressure

10. Vibration resistance: no separation or no disassembly

11. Chemicals resistance: insoluble to most solvents

12. Oxidation: inoxidizable

13. Liquidity: illiquidity, deformable to pressure

14. Period for performance guarantee: over 20 years at room temperature

The basic model of the conventional optical fiber connectors is theFC-type for indoor use, and a retention mechanism is added dependingupon application. For example, a water-resistant optical fiber connectoruses a sealing material applied over the external of the FC-type. Tosolve the third problem, the aforementioned silicone lowcrosslinking-density gel is used in the junction of two optical fiberwires as a junction conductor. For example, in the FC-type, the siliconelow crosslinking-density gel is enclosed in the connection space of theoptical fiber wires fitted with the ferrules for connecting to theadapter. This can provide an all-weather optical fiber connector havingan optical transmittance of 99% or more and a connection loss of 0.02 dBfor any variation of external environment without any change of the sizeof the connector or any additional structure or mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinally sectional view showing an embodiment of anoptical fiber connector, wherein a plug has the same structure on theright side and the left side thereof, and thereby only one of the sidesis illustrated;

FIG. 2 is a horizontal sectional view showing an embodiment of thecoupling portion of an adapter and a plug; and

FIG. 3 is an external view of a constitutional unit of an optical fiberconnector, or a schematic view of a measuring apparatus A according toone embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described withreference to the drawings.

In FIG. 3, the connection of an optical fiber connector comprises fourplugs A and one adapter B.

In FIG. 1, the plug A comprises a ferrule 1, a cylindrical rotatableferrule holder 2 to which the ferrule 1 is attached, a case 5 forhousing the ferrule holder 2, a buffer coil spring 6, and a rotatingouter ring 4. The ferrule holder 2 includes a rotation stopper portion33 having a regular octagon-shaped cross-section and a flange 3 forreceiving the buffer coil spring at the ferrule-mounting portion of theferrule holder 2. The ferrule holder 2 also includes a polygonal shaftportion 38 for attaching an optical fiber wire at the rear end of theferrule holder 2. The case 5 includes a pair of coupling guideside-grooves 36 and a pair of coupling elongated-holes 34, a pair ofcoupling-release push springs 7 extending in the middle of the pair ofcoupling elongated-holes 34, respectively, in an opposed relationshipwith each other. After the ferrule holder 2 is fitted into the case 5,the rotating outer ring 4 is press-fitted into the rear end of theferrule holder 2. An optical fiber wire 21 and an optical fiber corewire 22 are retained by the ferrule 1 and the ferrule holder 2.

The adapter B will now be described with reference to FIGS. 1 and 2.

The pair of ferrules 1 opposed to each other are retained by a sleeve11. A shell 12 housing the sleeve 11 is split into two and the innerwall of the shell 12 is formed in an octahedron to retain the sleeve 11.The shell 12 is also formed with elastic rotation stopper plates 13symmetric with respect to the axis to contact closely with two faces ofthe octahedron of the rotation stopper portion 33, respectively,provided at the ferrule-mounting portion of the ferrule holder 2. Theelastic rotation stopper plate 13 is provided at each of both ends ofthe shell 12 at given opposed positions. A space 37 for allowing theelastic rotation stopper plate to be bent is provided between the outerwall of the elastic rotation stopper plate 13 and the inner wall of anadapter body 14. The adaptor body 14 is provided with a pair ofengagement stems each having a coupling hook 15 and a pair ofpositioning guides 16 at given positions of both ends of the adapterbody 14. The pair of engagement stems are engaged with the elongatedholes 34 of the case 5 of the plug A, respectively. The pair ofpositioning guides 16 are fitted into the coupling side-grooves 36 ofthe plug A, respectively. The adapter B is completed by inserting theshell 12 into the adapter body 14 and fixing by a knock pin 17.

In FIG. 2, a silicone low crosslinking-density gel 41 is enclosed byapplying the silicone low crosslinking-density gel 41 on the end 31 ofthe ferrule with an optical fiber bonding material injection device,inserting the pair of plugs A from both inserting ports of the adapter Bto couple the pair of plugs A.

In FIG. 1, for coupling the adapter B with the plug A, the ferrule 1protruding from the front end of the plug A is inserted into aninsertion port opened at the center of the adapter B, and pushed thereinwith matching the positioning guide of the adapter B with the couplingguide side-groove 36 of the plug A. Then, the engagement stems eachhaving the hook 15 are moved in conjunction with the ferrule 1 and areengaged with the coupling elongated-holes 34 provided in the case 5serving as a coupling portion with the plug A, respectively.

In FIG. 1, for releasing the connection between the adapter B and theplug A, the coupling-release springs 7 provided in the case 5 are pushedinward to release the hooks of the latching sticks 15, and the plug A isthen pulled out to complete the releasing operation.

With reference to FIGS. 1 and 2, an axes positioning mechanism forcorrecting the displacement of the axes of an optical fiber wire 21 andanother optical fiber wire 21 will be described.

In FIG. 2, a pair of ferrules 1 each fitted with an optical fiber wires21 and a pair of ferrule holders 2 are positioned opposed to each otherthrough the adapter B. In this state, the both axes of the pair ofoptical fiber wires 21 are hardly aligned with each other. Thesepositions are corrected by simultaneously rotating each of the rotatingouter rings 4 of the ferrule holders 2. More specifically, for stoppingand retaining the ferrule holders 2, the two faces of the rotationstopper portion 33 formed in the polygonal cross-section provided at theferrule-mounting portion are closely contacted with and pressed by theelastic rotation stopper plate 13 provided in the shell 12 housed in theadapter body 14. In this state, when the rotating outer rings 4 providedin the ferrule holders 2 are rotated, the rotation stopper portions 33formed in the polygon are also rotated. At this moment, the elasticrotation stopper plate 13 is bent outwardly by the corners of therotation stopper portion 33 formed in the polygon to allow the rotationstopper portion 33 to be rotated. Then, the rotation stopper portion 33is stopped when the elastic rotation stopper plate 13 is contacted withone flat face of the polygon. That is, the displacement of the axes ofthe optical fiber wires 21 can be corrected with coupling the plug A tothe adapter B by allowing the elastic rotation stopper plate 13 to bebent in the space 37 between the elastic rotation stopper plate 13 andthe inner wall of the adapter body 14 with a length of one fifteenth ofone side of the polygon, and by rotating the rotating outer rings 4provided at the rear end of the ferrule holder 2.

With reference to FIGS. 2 and 3, how to confirm the correction of thedisplacement of the axes of the optical fiber wires 21 will bedescribed.

When the adapter B and the pair of plugs A are coupled and a siliconelow crosslinking-density gel is enclosed, the pair of plugs A2, A4 beingfree are connected to an entrance (transmit section) and an outlet(receive section) of a measuring device, respectively. Then, the pair offerrule holders 2 connected to the adapter B are rotated by rotating therotating outer rings 4 in increments of one notch as confirming thevalue of connection loss displayed on the measuring device, and the pairof ferrule holders 2 are stopped at a position where the optimum valueis displayed. The measuring device used for this adjustment may be aportable optical multimeter used in on-site application or an opticalmultimeter for research.

In the axes positioning mechanism for correcting the displacement of theaxes of the optical fiber wires, the rotation stopper portion providedin each of the ferrule holders has been arranged in a regular octagoncross-section. However, if a fine adjustment is necessary, the number ofpolygon may be increased. In case of the odd number of polygon, thenumber of the rotation stopper plate will be one.

In the axes positioning mechanism for correcting the displacement of theaxes of the optical fiber wires, the elastic rotation stopper plate hasbeen attached to the adapter body. However, the present invention is notlimited to this embodiment, and the elastic rotation stopper plate maybe attached to the ferrule holder. In this case, it would be able toapply to existing optical fiber connectors specified in JIS C5970 or thelike whereby the rotation stopper portion and rotation stopper platewhich are provided in the ferrule holder are located on the oppositeside with respect to the plug.

The two faces of the rotation stopper portion 33 formed in the polygoncross-section provided at the ferrule-mounting portion are closelycontacted with and pressed by the elastic rotation stopper plate 13provided in the shell 12 housed in the adapter body 14.

The ferrule holder has been constructed by integrating theferrule-mounting portion, the rotation stopper portion, the bufferspring receiving flange and the polygonal shaft portion, and pressingthe rotating outer ring into the polygonal shaft portion. Alternatively,the ferrule-mounting portion from may be separated from the bufferspring receiving flange, and other parts may be integrated to form afunctional holder. In this case, a ferrule holder may comprise theferrule-mounting portion and the buffer spring receiving flange, whichare fixed by female and male threads. While each component of the aboveembodiment has been formed of light alloy, any suitable engineeringplastics having substantially the same strength may be substituted forsuch a material.

While the case has been molded by using ABS resin which is one of theengineering plastics, and the coupling-release push spring attached tothe case has been formed of a blade spring, any suitable engineeringplastic having a resilient and high impact-resistance may be substitutedfor such an engineering plastic to integrate the case and the spring.This contributes to weight reduction.

In the adapter, the adapter body, the engagement stem with coupling hookand the positioning guide attached to the adapter body are integrallymolded by using POM resin which is one of elastic engineering plastics.The shell is split into two, and each of the ends of the shell has theelastic rotation stopper plates. When the pair of split shells arecoupled, the space housing the sleeve is a polygon. The shell and theelastic rotation stopper plates are also integrally molded by using POMresin which is one of elastic engineering plastics.

The adapter is coupled with the plug through one-touch operation, i.e.by matching the coupling guide side-grooves of the plug with thepositioning guide of the adapter and pushing the plug into the adapter.The coupling is released by pushing the coupling-release push spring ofthe plug and pulling out the plug.

Using an optical fiber bonding material injection device for enclosingthe silicone low crosslinking-density gel in the connection space makesa substantial contribution to enclosing with high accuracy and reducingworking hours. It takes only ten seconds to completely enclose thesilicone low crosslinking-density gel for one junction.

Each of the adapter and the plug according to the present invention isformed in a given cylindrical external shape. Thus, if a part of thiscylinder is concaved to form a mounting portion and a housing for thiscylinder is provided, a two-core or multiple-core plug, or adistribution box for connecting another optical fiber wires is easilyformed. A shaft portion having a polygon cross-section is formed in apart of ferrule holder forming this plug, so as to provide a mountingportion for fitting into the housing.

While each outer shape of the adapter and the ferrule holder has beenformed in a cylindrical shape, the present invention is not limited tosuch a shape, and it is apparent to use a polygonal shape.

INDUSTRIAL APPLICABILITY

The present invention is constructed as described above, and thus hasthe following effects.

The following experimental result shows the comparison of eachconnection loss of a single-mode FC-type optical fiber connector (theferrule has a planar-polished end) and an optical fiber connectormechanism according to the present invention. Generally, the connectionloss of the single-mode FC-type optical fiber connector be described as0.2 dB/m or less. The five samples of the FC-type optical fiberconnectors on the left side have been selected from 20 measured samplesin five different levels of connection loss. The connection losses onthe right side was measured by fabricating an adapter in the opticalfiber connector mechanism according to the present invention to matchwith the plug of the above FC-type optical fiber connector, and applyingthe silicone low crosslinking-density gel to the fabricated fivesamples.

Unit: dB Experimental Result Connection loss of optical fiber Connectionloss of FC-type connector mechanism according to the Optical fiberconnector present invention Sample 1 0.0999 +0.0204 2 0.1819 0.0009 30.2840 0.0033 4 0.6611 0.0116 5 0.8196 0.0153 Reference 6 1.3828 0.0155

From the above comparison of the connection loss, it is proved that theconnection loss gets close to zero excepting the transmission loss ofthe optical fiber itself by simultaneously implementing the axespositioning mechanism for correcting the displacement of the axes of theoptical fiber wires and the silicone low crosslinking-density gel as ajunction conductor capable of minimizing the connection space for themechanism. The values of samples 1 and 2 on the left side are rangedwithin the connection loss of 0.2 dB/m specified in the FC-type opticalfiber connectors. As shown the corresponding values according to thepresent invention on the right side, the connection loss values areranged within 0.001 dB/m, and thus the connection loss value can getalmost close to zero. The optical transmittance of the left side is95.4992%, while the optical transmittance on the right side according tothe present invention is 99.9978%. While the samples 3 and 4 are out ofthe specification, each connection loss of the samples 3 and 4 accordingto the present invention can be ranged within 0.02 dB. The largestconnection loss of the samples out of the specification is 0.6611 dB andthe corresponding optical transmittance is 85.8795%, while the opticaltransmittance according to the present invention is 99.5405%. In thesample 5 and the reference 6, the finishing process in the polishingprocesses was omitted. In this case, the optical fiber connectormechanism according to the present invention can also achieve theconnection loss within 0.02 dB. The reason why the sample 1 exhibitedpositive value is that the performance of the master cord exceeds, andit is not the result from amplification by the silicone lowcrosslinking-density gel. Each length of the samples was 3 m.

Then, three samples having the connection loss of 0.2 dB/m or less wererandomly selected from the 20 FC-type optical fiber connector samples,and the connection loss of the coupled samples having the connectionloss of 0.0999 dB, 0.1888 dB and 0.1931 dB, respectively, was measured.The number of junctions is three, and the sum of the connection loss was0.8758 dB. When the above two techniques according to the presentinvention are simultaneously implemented at the three junctions by usingthe aforementioned adapter, the sum of the connection loss was 0.0327dB. The optical transmittance on the left side is 81.7372%, whereas theoptical transmittance of the optical fiber connector mechanism accordingto the present invention is 99.2498%.

Further, only the split sleeve was used as a substitute for the adapter,and the plug was inserted into the sleeve. Then, the silicone lowcrosslinking-density gel was injected in the open connection space, andthe sleeve and adapter were dropped into the water. Then, the connectionloss was measured with exposing the silicone low crosslinking-densitygel in the water. This measured value was stable regardless of the lapseof time. This demonstrates an optimum function of preventing anyfunctional deterioration due to invaded dust and vapor, andcondensation. Thus, by using the silicone low crosslinking-density gel,the application can be expanded without changing the structure of theexisting optical fiber connector.

Each connection loss of the fusion bonding technique and fixedconnecting technique is specified as 0.01 dB/m. Thus, this requirementwill be sufficiently satisfied by simultaneously implementing the twotechniques according to the present invention.

What is claimed is:
 1. An optical fiber connector comprising: a first plug for retaining a first optical fiber core wire having a first optical fiber wire coaxially therein with protruding said first optical fiber wire from said first plug; a second plug for retaining a second optical fiber core wire having a second optical fiber wire coaxially therein with protruding said second optical fiber wire from said second plug; an adapter for coupling said first and second plugs with opposing each end of said first and second optical fiber wires, wherein each of said first and second plugs includes a ferrule holder fitted with a ferrule for retaining the optical fiber wire and a case for housing said ferrule holder; at least one of said ferrule holders of said first and second plugs is rotatably supported about the axis of the corresponding case with respect to the corresponding case, wherein said rotatably supported ferrule holder includes a rotation stopper portion formed in a part thereof, said rotation stopper portion having a polygon cross-section; a rotation stopper plate selectively engaging with a plurality of faces formed on the outer periphery of said rotation stopper portion, said rotation stopper plate having elasticity, wherein said rotation stopper plate is adapted to elastically engage selectively with one of said plurality of faces so as to define the rotational position of said ferrule, wherein said rotation stopper plate is attached to said adapter, and wherein said rotation stopper portion is formed at the end of said rotatably supported ferrule holder opposed to said adapter.
 2. An optical fiber connector as defined in claim 1, wherein said adapter includes a shell through which said ferrule is rotatably inserted, wherein said rotation stopper plate is attached to extend from one end of said shell opposed to said rotation stopper portion toward said rotation stopper portion.
 3. An optical fiber connector as defined in claim 2, wherein said shell includes a sleeve having both ends through which said ferrules of said first and second plugs are inserted, respectively.
 4. An optical fiber connector as defined in claim 3, which further includes a space through which said first and second optical fiber wires are opposed to each other, said space defining a connection space in said sleeve, wherein said connection space is filled with a transparent silicone low crosslinking-density gel having a refractive index substantially equal to that of said optical fiber wires.
 5. An optical fiber connector as defined in claim 1, which further includes a space through which said first and second optical fiber wires are opposed to each other, said space defining a connection space, wherein said connection space is filled with a transparent silicone low crosslinking-density gel having a refractive index substantially equal to that of said optical fiber wires.
 6. An optical fiber connector as defined in claim 1, wherein each of said ferrule holders of said first and second plugs is rotatably supported about the axis of the corresponding case with respect to the corresponding case.
 7. An optical fiber connector as defined in claim 1, which further includes a rotating outer ring fixed to the outer periphery of said rotatably supported ferrule holder, said rotating outer ring being adapted to be rotate so as to rotate said ferrule holder. 